1. Field of the Invention
The present invention relates generally to methods for preparing granular weed control products and, more particularly, to methods for improving the distribution of agriculturally active ingredients on such granular products.
2. Description of Related Art
Granular weed control products have been known in the consumer lawn industry which utilize systemic herbicides such as 2,4-D and MCPP-p for foliar application to broadleaf post-emergent weeds such as dandelions for purposes of killing the weeds. The active ingredients used in preparing these products are generally applied to inert carriers or fertilizer granules as a solid powder or a liquid solution. The level of active ingredient (AI) applied to the granular material is generally based on a specific total weight percentage of the entire product formulation. Normally, the resulting granular materials are then applied to a treated weed by using a spreader such as a broadcast spreader to spread the granules on the surface of the weed in a manner such that the individual granules or particles adhere to moist foliage in order to solubilize the active ingredient (AI), thus allowing it to enter the weed cells and kill the plant.
When a homogeneous sample of a typical weed control product is analyzed for active ingredient (AI) content the overall weight percentage obtainable is the key parameter of focus. However, the distribution of the active ingredient (AI) on the surface of the granules is generally not evaluated or specifically controlled.
As a result of this lack of distribution control, some granules have active ingredient (Ai) coatings with thicknesses and/or concentrations greater than can be solubilized by available moisture which, in most cases, comprises morning dew. The literature suggests that a moderate morning dew, during the spring time can deposit on average 30 mg/cm2 of water, with a thickness of about 0.3 mm. This factor is generally not taken into consideration when determining how AI is applied to the fertilizer and inert carrier surface.
However, since weeds transport the available active ingredient (AI) into their cell structure on the basis of a concentration gradient, the amount of active ingredient (AI) that can be solubilized will be transported into the weed. To the contrary, if a granular or particulate product has a thick coating of active ingredient (AI) and there is insufficient moisture available to dissolve or solubilize the excess active ingredient, that excess amount of active ingredient will not be transported into the weed and will be essentially lost for purposes of treating the plant.
Such active ingredient loss can lead to inconsistent and generally lower weed control and inefficient utilization of active ingredients. Thus, in view of the problems encountered in controlling the distribution of active ingredient on the granular surfaces, many prior weed control formulations have included significantly greater concentrations of active ingredient than would be necessary if processes had been available for controlling the distribution of active ingredient on the granular surface.
Agricultural formulations can be applied to plants in the form of solids, solutions, emulsions, suspensions, dispersions and the like, and are used in agriculture for applying agriculturally active chemicals to plants, soil, insects and the like. Among typical agricultural chemicals are pesticides such as herbicides, insecticides, fungicides, growth regulators and the like. Other typical agricultural chemicals include plant nutrients and micronutrients.
In particular, agricultural formulations containing herbicides either as solid powders or liquid solutions can be applied to granular material and the herbicides coated on the granules to be applied to weed foliage to control the weed plants. Normally, the coated granules are applied either in a liquid spray application or in a granular solid application to moist weed foliage using a spreader such as a broadcast spreader, with the individual granules desirably adhering to the moist foliage to solubilize the active herbicidal ingredient, allowing the active ingredient to enter the weed cells and to kill the plant.
Exemplary of relevant prior art in this field is U.S. Pat. No. 5,006,158 which discloses that diverse active herbicidal compounds or salts disclosed therein can be formulated as granules of relatively large particle size, as wettable powders, as emulsifiable concentrates, as powdery dusts, as flowables, as solutions or as any of several other known types of formulations, depending upon the desired mode of application. The formulations containing the actives are disclosed to contain as little as about 0.5% to as much as about 95% or more by weight of active ingredient. A herbicidally effective amount of the actives is disclosed as depending upon the nature of the seeds or plants to be controlled and the rate of application varies from about 0.01 to approximately 10 pounds per acre, preferably from about 0.02 to about 4 pounds per acre.
Granular formulations wherein the actives are carried on relatively coarse particles as disclosed in U.S. Pat. No. 5,006,158 are usually applied without dilution to the area in which suppression of vegetation is desired. Typical carriers for such granular formulations as described in U.S. Pat. No. 5,006,158 include sand, fuller's earth, attapulgite clay, bentonite clays, montmorillonite clay, vermiculite, perlite and other organic or inorganic materials which absorb or which may be coated with the toxicant. These granular formulations are normally prepared to contain about 0.1% to about 25% of active ingredients which may include surface-active agents such as heavy aromatic naphthas, kerosene or other petroleum fractions, or vegetable oils; and/or stickers such as dextrins, glue or synthetic resins.
In U.S. Pat. No. 6,890,889, herbicidal formulations comprising agriculturally active ingredients in combination with an adjuvant system were disclosed to optimize post emergent activity on broadleaved weeds in corn. The preferred adjuvant system to optimize weed control and minimize crop response was disclosed to be a crop oil concentrate (COC). Other adjuvant systems for use in the formulation may comprise liquid compositions such as methylated seed oil (MSO), urea ammonium nitrate (UAN) and ammonium sulfate (AMS). No granular formulations are disclosed.
In Published U.S. Patent Application US 2005/0096226, herbicidal compositions useful for controlling weeds in growing crops such as maize (corn) comprising triketone products including mesotrione in combination with an organic phosphate, phosphonate or phosphinate adjuvant were disclosed which can be prepared as a pre-mix concentrate for formulation in various forms including granular formulations with typical carriers such as sand, fuller's earth, attapulgite clay, bentonite clays, montmorillonite clay, vermiculite, perlite and other organic or inorganic materials which absorb or which can be coated with the active compound.
Thus, when a typical weed control product is analyzed for active ingredient content, the overall weight percentage of active ingredient (AI) obtainable from the product normally is the key parameter considered. However, the distribution of the active ingredient on the surface of the granules has generally not been evaluated or specifically controlled and methods for adequately providing such control have not been available. This lack of distribution control in the production processes has resulted in significant quantities of granules having active ingredient coatings with thicknesses and/or concentrations greater than the level that can be solubilized by the available moisture, which in most cases is the morning dew. The literature suggests that moderate morning dew in the spring in the United States can deposit on average 30 mg/cm2 of water with a thickness of about 0.3 mm.
In foliar treatments, plants transport active ingredients into their cell structure based on a concentration gradient and only the amount of active ingredient that can be solubilized will be transported into the weed. Thus, if a granule has a thick coating of active ingredient and if there is insufficient moisture on a treated leaf to dissolve the available active ingredient present in the coating, the excess active ingredient in the coating will not be transported into the cell structure of the plant for purposes of enhancing the weed killing effect of the applied granular product.
In this regard, it should be noted that in addition to the economic disadvantages resulting from waste of active ingredients when excess concentrations of such active ingredients are applied on the foliar surface of a weed in order to assure maximum intake of solubilized actives, governmental restrictions in the U.S. and elsewhere must also be taken into consideration concerning the amount of active ingredient that can be applied for weed control. Such governmental regulations may preclude the use and/or sale of products which will provide excessive application rates of actives ingredients when applied to weed foliage.
Thus, it has been a continuing problem in the art to provide methods for production of granular weed control products having relatively uniform distribution of active ingredients applied on the granules. In the absence of such methods, significant economic and functional problems have been encountered with the granular products produced employing methods which do not provide adequate distribution control capabilities. Such lack of distribution control can result in products that exhibit inconsistent and generally lower weed control and inefficient utilization of active ingredients including use of significantly greater concentrations of the active ingredients to achieve desired levels of weed control and these quantities may exceed governmental standards.
It would be advantageous to provide methods for producing granular agricultural products having improved control of the distribution pattern of active ingredients on such granular products.
Additionally, it would be advantageous to provide methods for improving the distribution of active ingredient (AI) on the surface of a weed control granule enabling reduction of the thickness of the active ingredient coating.
It also would be advantageous to provide methods for minimizing the potential for AI supersaturation in a granular weed control product and maximizing transport of the active ingredient (AI) on the granular product into the plant cells to cause effective kill of treated weeds.